The ability to reduce the surface tension of water is of great importance in waterborne coatings, inks, adhesives, and agricultural formulations because decreased surface tension translates to enhanced substrate wetting in actual formulations. Surface tension reduction in water-based systems is generally achieved through the addition of surfactants. Performance attributes resulting from the addition of surfactants include enhanced surface coverage, fewer defects, and more uniform distribution. Equilibrium surface tension performance is important when the system is at rest. However, the ability to reduce surface tension under dynamic conditions is of great importance in applications where high surface creation rates are utilized. Such applications include spraying of coatings or agricultural formulations, or high speed gravure or ink-jet printing. Dynamic surface tension is a fundamental quantity which provides a measure of the ability of a surfactant to reduce surface tension and provide wetting under such high speed application conditions.
Traditional nonionic surfactants such as alkylphenol or alcohol ethoxylates, and ethylene oxide (EO) propylene oxide (PO) copolymers have excellent equilibrium surface tension performance but are generally characterized as having poor dynamic surface tension reduction. In contrast, certain anionic surfactants such as sodium dialkyl sulfosuccinates can provide good dynamic results, but these are very foamy and impart water sensitivity to the finished coating.
The objective of this invention is to provide a family of surfactants which provide good equilibrium and dynamic surface tension properties and are low-foaming and would be widely accepted in the coating, ink, adhesive, and agricultural formulation industries.
The importance of reducing equilibrium and dynamic surface tension in applications such as coatings, inks, and agricultural formulations is well-appreciated in the art.
Low dynamic surface tension is of great importance in the application of waterborne coatings. In an article, [Schwartz, J. "The Importance of Low Dynamic Surface Tension in Waterborne Coatings", Journal of Coatings Technology, September 1992] there is a discussion of surface tension properties in waterborne coatings and a discussion of dynamic surface tension in such coatings. Equilibrium and dynamic surface tension were evaluated for several surface active agents including the ethylene oxide adducts of acetylenic glycols. It is pointed out that low dynamic surface tension is an important factor in achieving superior film formation in waterborne coatings. Dynamic coating application methods require surfactants with low dynamic surface tensions in order to prevent defects such as retraction, craters, and foam.
Efficient application of agricultural products is also highly dependent on the dynamic surface tension properties of the formulation. In an article, [Wirth, W.; Storp, S.; Jacobsen, W. "Mechanisms Controlling Leaf Retention of Agricultural Spray Solutions"; Pestic. Sci, 1991, 33, 411-420], the relationship between the dynamic surface tension of agricultural formulations and the ability of these formulations to be retained on a leaf was studied. These workers observed a good correlation between retention values and dynamic surface tension, with more effective retention of formulations exhibiting low dynamic surface tension.
Low dynamic surface tension is also important in high-speed printing as discussed in the article "Using Surfactants to Formulate VOC Compliant Waterbased Inks" [Medina, S. W.,; Sutovich, M. N. Am. Ink Maker 1994, 72 (2), 32-38]. In this article, it is stated that equilibrium surface tensions (EST's) are pertinent only to ink systems at rest. EST values, however, are not good indicators of performance in the dynamic, high speed printing environment under which the ink is used. Dynamic surface tension is a more appropriate property. This dynamic measurement is an indicator of the ability of the surfactant to migrate to a newly created ink/substrate interface to provide wetting during high speed printing.
U.S. Pat. No. 5,098,478 discloses water-based ink compositions comprising water, a pigment, a nonionic surfactant and a solubilizing agent for the nonionic surfactant. Dynamic surface tension in ink compositions for publication gravure printing must be reduced to a level of about 25 to 40 dynes/cm to assure that printability problems will not be encountered.
U.S. Pat. No. 5,562,762 discloses an aqueous jet ink of water, dissolved dyes and a tertiary amine having two polyethoxylate substituents and that low dynamic surface tension is important in ink jet printing.
Although there have been numerous references to alkylated polyamines, it has not been recognized that such materials have the ability to reduce dynamic surface tension of aqueous solutions while contributing little foam to the system. This combination of properties would be of value in water-based coatings, inks, adhesives, and agricultural formulations. The following patents and publications relate to alkylated polyethyleneamines and their applications:
U.S. Pat. No. 4,126,640 and U.S. Pat. No. 4,195,152 disclose N--(C5-C8)alkyl polyamines, e.g., MIBK and MIAK reductive alkylates of diethylenetriamine: ##STR2## These materials are noted to be useful as curatives in high solids epoxy coatings because of their very low viscosity. Other suggested uses are in potting compositions, laminations, and adhesives.
Y. Murata and M. J. Ueda, Antibact. Antifung. Agents 1989, 17 (8), 371-375 disclose trihydrochlorides of N,N"-dialkyldiethylenetriamines of the form ##STR3## where R is a linear C8 or C10 alkyl group have been shown to have antimicrobial properties against dental plaque bacteria. This study showed that in vitro bactericidal activity tended to increase with the length of the N-substituted alkyl chain. These workers suggested that this phenomenon may mean that each compound acts as a cationic surfactant. There is no suggestion that these materials should be effective at reducing dynamic surface tension. Furthermore, there is no suggestion that the free bases should have any effect reducing either equilibrium or dynamic surface tension.